It looks like something out of a slightly unhinged cartoon artist's imagination – long snout, dagger-like canines and a powerful set of muscles with which to chew its insect food.

However, Cronopio dentiacutus is no Warner Brothers creation but a small ferret-like mammal that lived 94m years ago in what is now South America.

The fossilised remains of the skulls and jaws of Cronopio were found in Patagonia and are described in the journal Nature by a team of researchers led by Guillermo Rougier of the University of Louisville.

Cronopio belongs to a group of extinct mammals known as dryolestoids, said the researchers. Its discovery will help scientists track the emergence and spread of mammals around the world.

In an accompanying article, Dr Christian de Muizon of the Natural History Museum in Paris says it is rare to find the remains of mammals from the age of the dinosaurs between 250m and 65m years ago. In addition, they are most often known from isolated teeth or partial jaws – complete skulls or skeletons are an exceptional find.

"Our knowledge of the first two-thirds of mammalian evolution, which extends from the first record of a mammal about 220m years ago to the end of the Cretaceous period 65.5m years ago, is therefore terribly incomplete," wrote De Muizon.